1. Field of the Invention
The present invention relates to an encoded-data converting apparatus and method for efficiently converting data encoded by first encoding into data encoded by second encoding.
2. Description of the Related Art
In recent years, cameras have become digital, and some of them have begun to employ moving-picture encoding methods. For example, digital still cameras employ JPEG (Joint Photographic Experts Group) encoding in order to record still pictures. Also, Motion JPEG which performs video recording by consecutively encoding still pictures is becoming widely used.
In addition, with widespread use of personal computers, MPEG (Moving Picture Experts Group)-4 encoding, standardized by the International Organization for Standardization (ISO), has begun to be used as a method for exchanging and delivering video on the Internet.
MPEG-4 is an encoding method using inter-encoding, and is optimal for use on the Internet, etc., since it is suitable particularly for low bit rates, compared with conventional MPEG-1 and MPEG-2.
Similarly, it is desirable to use data encoded by Motion JPEG, for example, on the Internet similarly to an MPEG-4 bit stream.
Since Motion JPEG only uses intra-encoding without using inter-encoding, simply using Motion JPEG results in a data amount that is too large to be delivered on the Internet or the like.
Accordingly, a technique is required to convert Motion JPEG encoded data into an MPEG-4 bit stream. First, the Motion JPEG encoded data is temporarily decoded back to pixel level. Then, motion compensation may need to be performed, after which the stream must be re-encoded, thus requiring extensive encoding conversion processing. Also, the re-encoding may cause additional image deterioration in the re-encoded image data.
A technique of the related art for converting an MPEG-1 encoded bit stream into an MPEG-4 bit stream is disclosed in, for example, Japanese Patent Laid-Open No. 2001-238214. A technique of the related art for converting an MPEG-2 bit stream into an MPEG-4 bit stream is disclosed in, for example, Japanese Patent Laid-Open No. 2001-238218. However, a technique in which an encoding format only using intra-encoding without using inter-encoding, such as Motion JPEG, is converted into an encoding format using inter-encoding, such as MPEG-4, has not been proposed.